The overall objective of this ongoing work is to understand the molecular mechanisms controlling contraction and relaxation of the uterus and their regulation by hormones. This proposal focuses on two areas of regulation: phospholipase C (PLC) and Ca-activated K channels (KCa). To define the mechanisms of coupling the action of oxytocin (OT) to membrane PLC activation, immunoneutralization of potential coupling proteins, overexpression of constitutents, and reconstitution experiments are proposed. The role of phosphorylation in the regulation of GTPgammaS-stimulated PLC will be explored. The nature of the regulation of PLC activity and the expression of PLC isoenzymes and related G- proteins during pregnancy will be determined. The mechanisms by which relaxin activates KCa channels, measured by electrophysiology, will be probed by the use of kinase inhibitors, and the effect of relaxin on other K channels will be determined. The effect of overexpression of a mutant regulatory subunit of protein kinase A resulting in suppression of enzyme activity on PLC and KCa channel regulation will be determined. This study of the mechanism of hormonal coupling to PLC and K channels and the importance of the hormonal mileau in the expression of these pathways will yield important basic information which may influence the management of myometrial contractile activity.